/* ==========================================================================
   whaternion — shared lesson stylesheet
   One stylesheet for every lesson and reference sheet, so the course reads as
   one book rather than a pile of one-offs.

   Design notes
   - Wears the Impractical Instruments storybook brand: the design system is
     vendored under `assets/brand/` and imported below, so every colour, font
     and edge here comes from the same tokens the studio site uses. See
     `assets/brand/README.md` before editing anything in that directory.
       Voices, and where each one is used:
         display (Luckiest Guy)  page + section titles, buttons
         body    (Besley)        all running prose, tables, captions
         mono    (Courier Prime) labels, chrome, readouts, code
         hand    (Schoolbell)    the one hand-written aside per page
   - Tufte-ish underneath: generous margins, serif prose, wide figures.
   - Two convention accents used consistently across ALL lessons:
       Unity  = deepened bulb yellow  (--unity)
       glTF   = deepened turquoise    (--gltf)
     Both are brand hues taken dark enough to read as text. Never use them for
     anything else.
   - Axis colours are the universal X/Y/Z = red/green/blue, deliberately left
     outside the brand palette. Arrows are ALWAYS also labelled with text, so
     colour is never the only channel.
   - Light + dark. Dark is the brand's ops palette, which is flat by design:
     hairline borders, no paper shadows. Print styles at the bottom (reference
     sheets must print).
   ========================================================================== */

@import "brand/design-system.css";

/* ---------- tokens ----------
   The brand supplies --paper, --ink, --sky, --butter, --persimmon, the type
   families, the spacing/border/shadow scale. Everything below either names a
   brand token or is a brand hue taken to a value that survives on paper.

   Values are literal hex, not color-mix(), because `assets/viz3d.js` reads
   these properties and hands them straight to a canvas 2D context. */

:root {
  --ink-soft:   #4a4742;
  --ink-faint:  #857f76;
  --rule:       #d8d2c6;
  --rule-soft:  #ece7dc;
  --panel:      #fbf7ec;   /* butter, thinned to a page-safe panel */
  --panel-2:    #f4eedf;

  --unity:      #9c6b08;   /* --ii-yellow, deepened to text contrast */
  --unity-bg:   #fff6d6;
  --gltf:       #0f6f78;   /* --ii-turquoise, likewise */
  --gltf-bg:    #ddf1f2;

  --axis-x:     #c0392b;
  --axis-y:     #2e7d32;
  --axis-z:     #1f5fa8;

  --good:       #46783f;   /* --moss, deepened */
  --bad:        #b3261e;
  --warn:       #a8760a;

  /* Type: brand families under the names the rest of this file uses.
     --ui is the chrome voice (labels, controls, table heads); running text is
     always --serif. */
  --mono:  var(--font-mono);
  --serif: var(--font-body);
  --ui:    var(--font-mono);
  --hand:  var(--font-hand);

  --measure: 34rem;   /* prose column */
  --wide:    58rem;   /* figures may bleed to here */
}

@media (prefers-color-scheme: dark) {
  :root {
    /* The brand's night-time face is the Show Dashboard's ops palette. */
    --paper:      var(--ops-bg);
    --ink:        var(--ops-text);
    --ink-soft:   var(--ops-text-mid);
    --ink-faint:  var(--ops-text-dim);
    --rule:       var(--ops-border-soft);
    --rule-soft:  var(--ops-border);
    --panel:      var(--ops-panel);
    --panel-2:    #22262c;

    --sky:        #2f5261;   /* the storybook ground, after dusk */
    --butter:     #2f2a17;
    /* Persimmon at its paper value is too dark to label anything on #111.
       Lifting the token lifts --link with it: the brand defines one from
       the other, and custom-property substitution is live. */
    --persimmon:  #ff8a5c;
    --string:     var(--ops-error);
    --moss:       var(--ops-online);

    --unity:      #e8b33d;
    --unity-bg:   #2c2317;
    --gltf:       #70e0e5;   /* on dark the brand turquoise stands as-is */
    --gltf-bg:    #142a2c;

    --axis-x:     #e8695c;
    --axis-y:     #6cc46f;
    --axis-z:     #6ba3e8;

    --good:       #6cc46f;
    --bad:        #e8695c;
    --warn:       #e8b44d;

    /* Ops surfaces are flat. Keep the inked outlines, drop the paper drop. */
    --shadow-paper:     none;
    --shadow-paper-sm:  none;
    --shadow-paper-pop: none;
    --border-ink:      var(--border-w) solid var(--rule);
    --border-ink-thin: 2px solid var(--rule);
  }
}

/* ---------- reset-ish ---------- */

*, *::before, *::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  /* The masthead bleeds to the viewport edge with a 100vw-based negative
     margin, which overshoots by the width of a classic scrollbar. Clip it. */
  overflow-x: clip;
}

body {
  margin: 0;
  padding: 0 1.5rem 8rem;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--serif);
  font-size: var(--text-base);
  line-height: 1.62;
  font-kerning: normal;
  text-rendering: optimizeLegibility;

  /* Tufte layout, in plain block flow:

       ┌──────────────┬────────────────┐
       │ prose        │ figure bleed   │
       └──────────────┴────────────────┘

     The page is one centred column `--wide` across. Prose is capped at
     `--measure`; figures, tables and callouts get the full width. Everything
     therefore shares one left edge and wide things extend right.

     Deliberately NOT grid or flex. Blocks like <pre> that scroll sideways are
     scroll containers, and a scroll container's automatic minimum size is
     zero — as a grid or flex item it gets squashed flat by its own track.
     Block flow sizes them from their content and sidesteps that entirely. */
  max-width: var(--wide);
  margin-inline: auto;
}

/* Prose measure. Left/right margins stay 0 throughout, so the per-element
   `margin` shorthands further down cannot disturb the alignment. */
body > * { max-width: var(--measure); }

body > .masthead,
body > figure,
body > .callout,
body > .spec,
body > .formula,
body > .tbl-wrap,
body > .quiz,
body > .panes,
body > pre,
body > .lesson-foot,
body > .wide {
  max-width: none;
}

/* ---------- masthead ----------
   The studio site opens on a full-bleed sky band with poster caps over it.
   Same band here, achieved without touching a single page's markup: the
   negative margin pulls the header out to the viewport edges, and the
   matching padding puts its text back on the body's own left edge. */

.masthead {
  max-width: var(--wide);
  background: var(--sky);
  color: var(--paper);
  border-bottom: var(--border-w) solid var(--ink);
  margin-block: 0 2.75rem;
  margin-inline: calc(50% - 50vw);
  padding: 2.75rem calc(50vw - 50%) 2.5rem;

  /* Axis colours are a teaching channel, so the standfirst keeps them — but
     the page values are chosen for paper and go muddy on the sky ground.
     Tints, scoped to the band, keep both the coding and the contrast. */
  --axis-x: #ffb5a9;
  --axis-y: #bff0b6;
  --axis-z: #c3dcff;
}

/* The studio's hero kicker: a paper pill, hand-inked. */
.masthead .kicker {
  font-family: var(--ui);
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink);
  background: var(--paper);
  border: var(--border-ink-thin);
  border-radius: var(--radius-wobble-sm);
  padding: 0.4rem 0.85rem 0.3rem;
  margin: 0 0 1.1rem;
  display: inline-flex;
  gap: 0.6rem;
  align-items: baseline;
  flex-wrap: wrap;
}

.masthead h1 {
  font-family: var(--font-display);
  font-weight: 400;
  font-size: clamp(2.1rem, 5.6vw, 3.6rem);
  line-height: 0.98;
  letter-spacing: 0.01em;
  text-transform: uppercase;
  color: var(--paper);
  text-shadow: 4px 4px 0 rgba(0, 0, 0, 0.5);
  margin: 0 0 0.85rem;
  text-wrap: balance;
}

.masthead .standfirst {
  font-size: 1.15rem;
  line-height: 1.5;
  color: rgba(255, 255, 255, 0.92);
  margin: 0;
  max-width: 38rem;
  text-wrap: pretty;
}

.masthead a { color: var(--ii-yellow); }

/* ---------- prose ---------- */

/* Section heads are the studio's persimmon mono label with a trailing rule. */
h2 {
  font-family: var(--ui);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--persimmon);
  margin: 3.5rem 0 0.9rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}
h2::after {
  content: "";
  flex: 1;
  height: 2px;
  background: var(--ink);
  opacity: 0.18;
}

h3 {
  font-family: var(--font-display);
  font-weight: 400;
  font-size: 1.3rem;
  line-height: 1.15;
  letter-spacing: 0.015em;
  text-transform: uppercase;
  color: var(--ink);
  margin: 2.4rem 0 0.5rem;
  text-wrap: balance;
}

h4 {
  font-family: var(--ui);
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin: 1.75rem 0 0.35rem;
}

p { margin: 0 0 1.1rem; text-wrap: pretty; }

a {
  color: var(--link);
  text-decoration-thickness: 2px;
  text-underline-offset: 0.16em;
  text-decoration-color: color-mix(in srgb, currentColor 45%, transparent);
}
a:hover { text-decoration-color: currentColor; }

strong { font-weight: 700; }

em { font-style: italic; }

code, kbd, samp {
  font-family: var(--mono);
  font-size: 0.9em;
  background: var(--panel);
  border: 1px solid var(--rule);
  border-radius: var(--radius-sm);
  padding: 0.06em 0.32em;
}

pre {
  font-family: var(--mono);
  font-size: 0.85rem;
  line-height: 1.6;
  background: var(--panel);
  border: var(--border-ink-thin);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-paper-sm);
  padding: 0.95rem 1.15rem;
  overflow-x: auto;
  margin: 0 0 1.5rem;
}
pre code { background: none; border: 0; padding: 0; font-size: inherit; }

ul, ol { margin: 0 0 1.2rem; padding-left: 1.35rem; }
li { margin-bottom: 0.4rem; }
li > ul, li > ol { margin-top: 0.4rem; margin-bottom: 0.3rem; }

hr {
  border: 0;
  border-top: 2px solid var(--rule);
  margin: 3rem 0;
}

blockquote {
  margin: 0 0 1.25rem;
  padding: 0.1rem 0 0.1rem 1.1rem;
  border-left: 3px solid var(--rule);
  color: var(--ink-soft);
  font-style: italic;
}
blockquote p:last-child { margin-bottom: 0; }

/* ---------- the spec quote: primary-source evidence ----------
   Turquoise drop shadow — the brand's "pop" — so quoted spec text is visibly
   a different kind of thing from the lesson's own voice. */

.spec {
  max-width: var(--wide);
  margin: 1.75rem auto 2rem;
  padding: 1.1rem 1.3rem;
  background: var(--paper);
  border: var(--border-ink-thin);
  border-radius: var(--radius-wobble-sm);
  box-shadow: var(--shadow-paper-pop);
  font-size: 1rem;
}
.spec .src {
  display: block;
  font-family: var(--ui);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--persimmon);
  margin-bottom: 0.6rem;
}
.spec q { font-style: italic; }
.spec p:last-child { margin-bottom: 0; }

/* ---------- convention badges (Unity / glTF) ---------- */

.tag {
  font-family: var(--ui);
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  padding: 0.16em 0.5em;
  border-radius: var(--radius-sm);
  white-space: nowrap;
  vertical-align: 0.08em;
}
.tag.unity { color: var(--unity); background: var(--unity-bg); border: 1px solid color-mix(in srgb, var(--unity) 40%, transparent); }
.tag.gltf  { color: var(--gltf);  background: var(--gltf-bg);  border: 1px solid color-mix(in srgb, var(--gltf) 40%, transparent); }

/* Marks a table row we rely on but could not trace to a quotable sentence.
   The whole point of the reference sheet is that it settles arguments, which
   an uncited row cannot do — so it says which rows those are. */
.uncited {
  color: var(--ink-faint);
  font-weight: 700;
  cursor: help;
}

.ax { font-family: var(--mono); font-weight: 700; }
.ax.x { color: var(--axis-x); }
.ax.y { color: var(--axis-y); }
.ax.z { color: var(--axis-z); }

/* ---------- figures ----------
   Each figure is an inked plate, the same card the studio site hangs its
   photographs in. Corners stay a plain radius rather than the wobble: the
   canvas draws to its own edges and a blob radius would crop the geometry. */

figure {
  max-width: var(--wide);
  margin: 2.25rem auto 2.5rem;
}

figure canvas {
  display: block;
  width: 100%;
  background: var(--panel);
  border: var(--border-ink-thin);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-paper-sm);
  touch-action: none;
  cursor: grab;
}
figure canvas.dragging { cursor: grabbing; }

figcaption {
  font-family: var(--serif);
  font-size: 0.92rem;
  line-height: 1.5;
  color: var(--ink-soft);
  margin-top: 0.85rem;
  text-wrap: pretty;
}
figcaption b { color: var(--ink); font-weight: 700; }

/* two panes side by side — the workhorse layout of this course */
.panes {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}
@media (max-width: 44rem) {
  .panes { grid-template-columns: 1fr; }
}

/* A grid item defaults to min-width:auto, whose automatic minimum is the
   item's min-content size. Put a horizontal scroll container in one — a
   `.readout`, a `pre`, a `.tbl-wrap` — and the column grows to the content's
   full width instead of scrolling, overflowing the grid. (Measured: 920px of
   readout in an 880px `.panes` row.) This is the INLINE-axis half of the
   gotcha in NOTES.md, and it is the half that bites here.

   Applied to every column rather than to `.pane`, so a lesson that drops a
   bare <div> into a `.panes` row cannot reintroduce it. */
.panes > * { min-width: 0; }

.pane > .pane-hd {
  font-family: var(--ui);
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  margin-bottom: 0.5rem;
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 0.5rem;
}
.pane.unity > .pane-hd { color: var(--unity); }
.pane.gltf  > .pane-hd { color: var(--gltf); }
.pane.unity canvas { border-color: var(--unity); }
.pane.gltf  canvas { border-color: var(--gltf); }
.pane-hd .note { font-weight: 400; letter-spacing: 0.02em; text-transform: none; color: var(--ink-faint); font-size: 0.72rem; }

/* ---------- callouts ----------
   Inked cards with a flat paper shadow. The shadow carries the meaning:
   ink for a plain aside, coral for a trap, moss for a win, and the key
   callout sits on butter so it reads as the page's one lit window. */

.callout {
  max-width: var(--wide);
  margin: 2rem auto;
  padding: 1.15rem 1.35rem;
  background: var(--panel);
  border: var(--border-ink-thin);
  border-radius: var(--radius-wobble-sm);
  box-shadow: var(--shadow-paper-sm);
  font-size: 1rem;
}
.callout > .hd {
  font-family: var(--ui);
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  margin-bottom: 0.55rem;
  color: var(--ink-faint);
}
.callout p:last-child, .callout ul:last-child, .callout ol:last-child { margin-bottom: 0; }

.callout.key {
  background: var(--butter);
  border: var(--border-ink);
  box-shadow: var(--shadow-paper);
}
.callout.key > .hd { color: var(--ink); }
.callout.key .big {
  font-size: 1.2rem;
  line-height: 1.45;
  font-weight: 700;
  margin-bottom: 0.7rem;
  text-wrap: pretty;
}

.callout.trap { box-shadow: 4px 4px 0 var(--string); }
.callout.trap > .hd { color: var(--bad); }

.callout.win { box-shadow: 4px 4px 0 var(--moss); }
.callout.win > .hd { color: var(--good); }

/* ---------- formula display ---------- */

.formula {
  max-width: var(--wide);
  margin: 1.5rem auto 1.75rem;
  padding: 1rem 1.2rem;
  background: var(--panel);
  border: var(--border-ink-thin);
  border-radius: var(--radius-md);
  font-family: var(--mono);
  font-size: 1rem;
  line-height: 1.9;
  text-align: center;
  overflow-x: auto;
}
.formula .lbl {
  display: block;
  font-family: var(--ui);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--persimmon);
  margin-bottom: 0.45rem;
}

/* ---------- tables ---------- */

.tbl-wrap { max-width: var(--wide); margin: 1.75rem auto 2rem; overflow-x: auto; }

table {
  width: 100%;
  border-collapse: collapse;
  font-family: var(--serif);
  font-size: 0.97rem;
}
caption {
  caption-side: bottom;
  font-family: var(--serif);
  font-size: 0.9rem;
  color: var(--ink-soft);
  text-align: left;
  padding-top: 0.7rem;
}
th, td {
  text-align: left;
  padding: 0.55rem 0.9rem 0.55rem 0;
  border-bottom: 1px solid var(--rule);
  vertical-align: top;
}
thead th {
  font-family: var(--ui);
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--persimmon);
  border-bottom: 2px solid var(--ink);
  white-space: nowrap;
}
tbody tr:last-child td { border-bottom: 0; }
td code { font-size: 0.85rem; }

/* ---------- footer / nav ---------- */

.lesson-foot {
  max-width: var(--wide);
  margin-top: 4rem;
  padding-top: 1.75rem;
  border-top: var(--border-w) solid var(--ink);
}

/* Cards that behave like the studio's call-to-action: lift into the
   turquoise on hover, press back down on click. */
.readnext {
  display: grid;
  gap: 1rem;
  grid-template-columns: repeat(auto-fit, minmax(15rem, 1fr));
  margin-bottom: 2.25rem;
}
.readnext a {
  display: block;
  padding: 1rem 1.15rem;
  background: var(--paper);
  border: var(--border-ink);
  border-radius: var(--radius-wobble-sm);
  box-shadow: var(--shadow-paper);
  text-decoration: none;
  color: var(--ink);
  font-family: var(--serif);
  font-size: 0.95rem;
  line-height: 1.45;
  transition: transform 0.08s ease, box-shadow 0.08s ease;
}
.readnext a:hover { transform: translate(-2px, -2px); box-shadow: 6px 6px 0 var(--ii-turquoise); }
.readnext a:active { transform: translate(2px, 2px); box-shadow: var(--shadow-paper-sm); }
.readnext a .lbl {
  display: block;
  font-family: var(--ui);
  font-size: 0.66rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--persimmon);
  margin-bottom: 0.35rem;
}
.readnext a b { font-weight: 700; }

/* The one hand-written aside per page. */
.ask {
  font-family: var(--serif);
  font-size: 0.97rem;
  line-height: 1.55;
  color: var(--ink-soft);
  background: var(--panel);
  border: 2px dashed var(--ink-faint);
  border-radius: var(--radius-wobble-sm);
  padding: 1rem 1.15rem;
  margin-bottom: 2rem;
}
.ask b {
  font-family: var(--hand);
  font-weight: 400;
  font-size: 1.35em;
  color: var(--persimmon);
}

.colophon {
  font-family: var(--ui);
  font-size: 0.78rem;
  letter-spacing: 0.03em;
  color: var(--ink-faint);
  line-height: 1.7;
}
.colophon a { color: var(--ink-soft); }

/* ---------- source list ---------- */

.sources { font-family: var(--serif); font-size: 0.94rem; line-height: 1.55; }
.sources li { margin-bottom: 0.55rem; color: var(--ink-soft); }
.sources li b { color: var(--ink); font-weight: 700; }

/* ---------- utility ---------- */

.wide { max-width: var(--wide); }
.center { text-align: center; }
.nowrap { white-space: nowrap; }
.small { font-size: 0.9em; }
.muted { color: var(--ink-soft); }
.sans { font-family: var(--ui); }

/* ==========================================================================
   controls (assets/ui.js)
   The instrument panel. This is the brand's ops voice — Courier, flat
   surfaces, hairline rules — sitting under the storybook plates.
   ========================================================================== */

.ctl-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: flex-end;
  gap: 1rem 1.5rem;
  margin-top: 0.9rem;
  padding: 0.9rem 1.05rem;
  background: var(--panel);
  border: var(--border-ink-thin);
  border-radius: var(--radius-md);
  font-family: var(--ui);
}

.ctl-bar-label {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--persimmon);
  align-self: center;
}

.ctl { display: flex; flex-direction: column; gap: 0.35rem; min-width: 0; }
.ctl-head { display: flex; align-items: baseline; justify-content: space-between; gap: 0.75rem; }

.ctl-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.09em;
  text-transform: uppercase;
  color: var(--ink-faint);
}

.ctl-value { font-family: var(--mono); font-size: 0.78rem; color: var(--ink); font-variant-numeric: tabular-nums; }

/* segmented radio group */
.seg { display: inline-flex; border: var(--border-ink-thin); border-radius: var(--radius-sm); overflow: hidden; background: var(--paper); }
.seg-item { position: relative; display: block; }
.seg-item:not(:last-child) { border-right: 2px solid var(--ink); }
.seg-item > span {
  display: block;
  padding: 0.34rem 0.75rem;
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--ink-soft);
  cursor: pointer;
  white-space: nowrap;
  user-select: none;
}
.seg-item > span:hover { background: var(--panel-2); color: var(--ink); }
.seg-item input:checked + span { background: var(--ink); color: var(--paper); }
.seg-item input { position: absolute; opacity: 0; pointer-events: none; }
.seg-item input:focus-visible + span { outline: 2px solid var(--gltf); outline-offset: -2px; }

.ctl-slider { min-width: 13rem; flex: 1 1 13rem; }
.ctl-slider input[type=range] { width: 100%; accent-color: var(--persimmon); margin: 0; }

.ctl-check { display: inline-flex; align-items: center; gap: 0.45rem; font-size: 0.84rem; cursor: pointer; color: var(--ink); }
.ctl-check input { accent-color: var(--persimmon); width: 1rem; height: 1rem; }

/* The studio's button: bulb yellow, inked, turquoise shadow, presses down. */
.ctl-btn {
  font-family: var(--font-display);
  font-size: 0.9rem;
  font-weight: 400;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  padding: 0.45rem 0.9rem 0.3rem;
  color: var(--ink);
  background: var(--ii-yellow);
  border: var(--border-ink-thin);
  border-radius: var(--radius-wobble-sm);
  box-shadow: var(--shadow-paper-sm);
  cursor: pointer;
  transition: transform 0.08s ease, box-shadow 0.08s ease;
}
.ctl-btn:hover { transform: translate(-2px, -2px); box-shadow: 4px 4px 0 var(--ii-turquoise); }
.ctl-btn:active { transform: translate(1px, 1px); box-shadow: 1px 1px 0 var(--ink); }
.ctl-btn:disabled { opacity: 0.4; cursor: default; transform: none; box-shadow: var(--shadow-paper-sm); }
.ctl-btn.subtle { background: var(--paper); color: var(--ink-soft); }
.ctl-btn.subtle:hover { color: var(--ink); }

/* live numeric readout */
.readout {
  font-family: var(--mono);
  font-size: 0.8rem;
  line-height: 1.75;
  background: var(--paper);
  border: var(--border-ink-thin);
  border-radius: var(--radius-sm);
  padding: 0.6rem 0.8rem;
  min-width: 0;
  overflow-x: auto;
}
.readout-label {
  display: block;
  font-family: var(--ui);
  font-size: 0.64rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--persimmon);
  margin-bottom: 0.35rem;
}
.readout-body { white-space: pre; font-variant-numeric: tabular-nums; }
.readout-body .k { color: var(--ink-faint); }

/* pass/fail strip */
.status { font-family: var(--ui); font-size: 0.82rem; display: flex; flex-direction: column; gap: 0.3rem; }
.status-row { display: flex; align-items: baseline; gap: 0.45rem; line-height: 1.45; }
.status-row.ok  { color: var(--good); }
.status-row.bad { color: var(--bad); }
.status-mark { font-weight: 700; width: 0.9em; flex: none; }
.status-text b { font-weight: 700; }
.status-detail { color: var(--ink-faint); font-size: 0.78rem; }

/* vector entry */
.vecin {
  display: inline-flex;
  align-items: center;
  gap: 0.15rem;
  font-family: var(--mono);
  font-size: 0.92rem;
  padding: 0.25rem 0.55rem;
  border: var(--border-ink-thin);
  border-radius: var(--radius-sm);
  background: var(--paper);
}
.vecin.ok  { border-color: var(--good); box-shadow: inset 0 0 0 1px var(--good); }
.vecin.bad { border-color: var(--bad);  box-shadow: inset 0 0 0 1px var(--bad); }
.vecin-label { font-family: var(--ui); font-size: 0.74rem; font-weight: 700; color: var(--ink-faint); margin-right: 0.35rem; }
.vecin-paren, .vecin-comma { color: var(--ink-faint); }
.vecin-box {
  width: 3.4rem;
  font-family: var(--mono);
  font-size: 0.92rem;
  text-align: center;
  color: var(--ink);
  background: transparent;
  border: 0;
  border-bottom: 2px solid var(--rule);
  padding: 0.1rem 0.15rem;
}
.vecin-box:focus { outline: none; border-bottom-color: var(--ink); }
.vecin-box:read-only { color: var(--ink-soft); border-bottom-style: dotted; }

.sr-only {
  position: absolute; width: 1px; height: 1px;
  padding: 0; margin: -1px; overflow: hidden;
  clip: rect(0 0 0 0); white-space: nowrap; border: 0;
}

/* ==========================================================================
   quiz (assets/quiz.js)
   ========================================================================== */

.quiz {
  max-width: var(--wide);
  margin: 2.5rem auto;
  padding: 1.4rem 1.5rem 1.5rem;
  background: var(--panel);
  border: var(--border-ink);
  border-radius: var(--radius-wobble);
  box-shadow: var(--shadow-paper);
}

.quiz-hd { display: flex; align-items: baseline; justify-content: space-between; gap: 1rem; margin-bottom: 0.5rem; }
.quiz-hd h3 { margin: 0; font-size: 1.25rem; }
.quiz-score {
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--ink-faint);
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
}

.quiz-intro { font-family: var(--serif); font-size: 0.95rem; color: var(--ink-soft); margin: 0 0 1rem; }

.quiz-list { display: flex; flex-direction: column; gap: 1.4rem; }

.quiz-q { padding-top: 1.2rem; border-top: 1px solid var(--rule); }
.quiz-q:first-child { padding-top: 0.4rem; border-top: 0; }

.quiz-prompt { display: flex; gap: 0.55rem; font-size: 1rem; line-height: 1.5; margin-bottom: 0.8rem; }
.quiz-num { font-family: var(--ui); font-weight: 700; color: var(--persimmon); flex: none; }

.quiz-opts { display: flex; flex-direction: column; gap: 0.5rem; }

.quiz-opt {
  display: block;
  width: 100%;
  text-align: left;
  font-family: var(--serif);
  font-size: 0.95rem;
  line-height: 1.45;
  padding: 0.6rem 0.85rem;
  color: var(--ink);
  background: var(--paper);
  border: var(--border-ink-thin);
  border-radius: var(--radius-wobble-sm);
  cursor: pointer;
  transition: transform 0.08s ease, box-shadow 0.08s ease;
}
.quiz-opt:hover:not(:disabled) { transform: translate(-2px, -2px); box-shadow: 3px 3px 0 var(--ink); }
.quiz-opt:disabled { cursor: default; transform: none; }
.quiz-opt code { background: var(--panel-2); font-size: 0.86em; }
.quiz-opt.ok  { border-color: var(--good); background: color-mix(in srgb, var(--good) 12%, var(--paper)); box-shadow: 3px 3px 0 var(--good); }
.quiz-opt.bad { border-color: var(--bad);  background: color-mix(in srgb, var(--bad) 12%, var(--paper)); box-shadow: 3px 3px 0 var(--bad); }
.quiz-opt.revealed { border-style: dashed; }
.quiz-opt:disabled:not(.ok):not(.bad) { opacity: 0.5; }

.quiz-vecrow { display: flex; align-items: center; gap: 0.7rem; flex-wrap: wrap; }

.quiz-fb {
  display: none;
  font-family: var(--serif);
  font-size: 0.95rem;
  line-height: 1.5;
  margin-top: 0.75rem;
  padding: 0.65rem 0.85rem;
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--rule);
  background: var(--paper);
  color: var(--ink-soft);
}
.quiz-fb.show { display: block; }
.quiz-fb.ok  { border-left-color: var(--good); }
.quiz-fb.bad { border-left-color: var(--bad); }
.quiz-fb b { color: var(--ink); font-weight: 700; }
.quiz-fb code { font-size: 0.86em; }

.quiz-foot { margin-top: 1.4rem; padding-top: 1.1rem; border-top: 2px solid var(--ink); }
.quiz-summary { font-family: var(--serif); font-size: 0.95rem; color: var(--ink-soft); margin: 0 0 0.8rem; }
.quiz-summary b { color: var(--ink); }

/* ---------- print (reference sheets must print well) ---------- */

@media print {
  :root {
    --paper: #fff; --ink: #000; --ink-soft: #333; --ink-faint: #555;
    --rule: #bbb; --rule-soft: #ddd; --panel: #f7f7f7; --panel-2: #f0f0f0;
    --unity-bg: #fff; --gltf-bg: #fff;
    /* Ink shadows and blob corners cost toner and page; print is flat. */
    --shadow-paper: none; --shadow-paper-sm: none; --shadow-paper-pop: none;
    --radius-wobble: 3px; --radius-wobble-sm: 3px;
    --border-w: 1px;
    --border-ink: 1px solid #000; --border-ink-thin: 1px solid #000;
  }

  @page { margin: 11mm; }

  /* Reference sheets are meant to end up on a desk, so print is tuned for
     density: one sheet, front and back, at a size still readable at arm's
     length. Verified by page-counting the generated PDF, not by eye. */
  body { padding: 0; max-width: 100%; font-size: 8.6pt; line-height: 1.3; }
  body > * { max-width: 100%; }

  p { margin-bottom: 0.5rem; }
  ul, ol { margin-bottom: 0.5rem; padding-left: 1.1rem; }
  li { margin-bottom: 0.12rem; }

  /* No sky band on paper: the header goes back to a ruled masthead, and the
     axis tints it scoped for the sky go back to their page values. */
  .masthead {
    background: none; color: #000;
    margin: 0 0 0.6rem; padding: 0 0 0.35rem;
    border-bottom: 1px solid #000;
    --axis-x: #c0392b; --axis-y: #2e7d32; --axis-z: #1f5fa8;
  }
  .masthead h1 { font-size: 15pt; margin-bottom: 0.25rem; color: #000; text-shadow: none; }
  .masthead .kicker {
    font-size: 6pt; margin-bottom: 0.3rem; color: #555;
    background: none; border: 0; padding: 0;
  }
  .masthead .standfirst { font-size: 9pt; line-height: 1.32; color: #333; }

  h2 { margin: 0.8rem 0 0.3rem; font-size: 7pt; page-break-after: avoid; }
  h3, h4 { margin: 0.55rem 0 0.15rem; font-size: 9pt; page-break-after: avoid; }

  .callout, .spec { margin: 0.6rem 0; padding: 0.5rem 0.65rem; font-size: 8.4pt; }
  /* The trap/win accent is a colour, not a slab of it: on paper the flat
     shadow becomes a rule down the left edge. */
  .callout.trap { box-shadow: none; border-left: 3px solid var(--string); }
  .callout.win  { box-shadow: none; border-left: 3px solid var(--moss); }
  .callout > .hd, .spec .src { font-size: 6.2pt; margin-bottom: 0.25rem; }
  .callout.key { background: #f2f2f2; }
  .callout.key .big { font-size: 9.4pt; margin-bottom: 0.3rem; }

  .formula { margin: 0.5rem 0; padding: 0.45rem 0.6rem; font-size: 9pt; line-height: 1.4; }
  .formula .lbl { font-size: 6.2pt; margin-bottom: 0.2rem; }

  pre { margin: 0.5rem 0; padding: 0.5rem 0.65rem; font-size: 7.4pt; line-height: 1.42; }

  .tbl-wrap { margin: 0.6rem 0; overflow: visible; }
  table { font-size: 8pt; }
  th, td { padding: 0.22rem 0.6rem 0.22rem 0; }
  thead th { font-size: 6.2pt; border-bottom: 1px solid #000; }
  caption { font-size: 7.2pt; padding-top: 0.35rem; }

  .sources { font-size: 7.2pt; line-height: 1.32; }
  .sources li { margin-bottom: 0.25rem; }

  .lesson-foot { margin-top: 0.9rem; padding-top: 0.5rem; border-top: 1px solid #000; }
  .colophon { font-size: 6.6pt; }

  /* Never split an atomic block across a page boundary. */
  figure, .callout, table, .formula, .spec, pre, .tbl-wrap { page-break-inside: avoid; }

  .no-print, .ask, .readnext, .quiz, .ctl-bar, .status, .readout { display: none !important; }

  a { text-decoration: none; color: #000; }
  /* Spell out link targets — a printed page cannot be clicked. */
  .sources a[href^="http"]::after {
    content: " (" attr(href) ")";
    font-size: 6.4pt; color: #666; word-break: break-all;
  }
}